You probably already do, if you have ever browsed the stacks of your local library where the Burroughs Mars novels are shelved.
It's Mahlon Blaine (1894 1969). Here's the first illustration that appears in the 1974 Canaveral Press edition of A Fighting Man of Mars:
And here's where I found it (and you can find the rest of his illustrations for that book there as well).
The illustrations are dated '62, so I just imagine that it was creepy weirdness like this that inspired all the psychedelic heads to make all that acid rock music down in San Francisco and over in Canterbury.